There is work ongoing within third generation partnership project (3GPP) Global System for Mobile communication/Enhanced Data rates for GSM Evolution (GSM/EDGE) Radio Access Network (GERAN) standardisation in order to introduce support for an Earthquake Tsunami Warning System (ETWS) The ETWS is designed to make it possible to quickly send notifications about coming earthquakes and/or tsunamis to mobile stations (MS). The mobile station is in turn configured to warn the user so that he/she can execute safety measures.
There are requirements to reach the users/mobile stations with a primary notification message within 4 seconds. In order to avoid that fake messages are received causing chaos, inclusion of authentication information in the primary notification will most likely be needed. An alternative that is discussed is to have authentication information in the form of a digital signature (e.g. 41 bytes if using DSA signatures).
Moreover, the mobile station in a GERAN network may be in different modes:
Idle mode, when the mobile station is currently neither used for any speech call or data service;
Dedicated mode, when the mobile station is currently used for a speech call or for a circuit switched data connection;
Packet transfer mode, when the mobile station is currently used for a packet switched data connection (GPRS);
Dual transfer mode, when the mobile station is currently (simultaneously) used for both a speech call and a packet switched data connection (GPRS).
When an ETWS primary notification needs to be sent out through the GERAN network, it is therefore necessary to reach the mobile station within the required time limit (e.g. 4 seconds as now discussed) independent of the mode the mobile station is currently in.
With the existing proposals for transmission of ETWS primary notifications within GERAN, proposed in 3GPP TDoc GP-080142 and 3GPP TDoc GP-081217, mobile stations that are in packet transfer mode can not be reached. In other words, mobile stations that are used for a packet switched service will not be reached by the ETWS warning even though they are in the affected area, where ETWS primary notifications are being transmitted through the GERAN network.
A proposal for transmission of ETWS primary notifications to mobile stations in dedicated mode has been presented in 3GPP TDoc GP-080142. The proposal is that when the Base Station Subsystem (BSS) receives an ETWS primary notification, which it shall transmit to mobile stations in a certain area, it builds point-to-point Short Message Service (SMS) messages containing the ETWS primary notification. Those SMS messages are then sent to the mobile stations in dedicated mode in the affected area through the Slow Associated Control Channel (SACCH). The same proposal would then probably also be used for mobile stations in dual transfer mode. However, there exist some problems with this proposed solution for dedicated mode and potentially also for dual transfer mode:
The use of an SMS (through the SACCH) would not be reliable in case of a simultaneous handover procedure. An ongoing SMS delivery will be interrupted and not re-sent if a handover procedure is triggered, moving the mobile to another cell. The mobile station would then not be reached by the ETWS primary notification.
The need to transmit the point-to-point SMS on the SACCH leads to a long distribution time for the ETWS primary notification.
Hence, there is a need for an improved method and device for transmitting an ETWS notification message in a GERAN system.